The present invention relates generally to apparatus for holding and transporting articles. In particular, the present invention relates to a fluid actuated, dual-piston transfer apparatus for holding and transporting an article.
Automated production line assemblies normally utilize transfer apparatus configured to automatically hold or grasp an article needed for the assembly of a product, and move or transport the article from a first location to a second, remote location. Once the article is transported to the second location, the transfer apparatus releases the article, retracts and subsequently repeats the process. The specific articles transported by these apparatus vary according to the particular industrial application. Frequently, transfer apparatus are used in the automated transportation of bolts, weld studs or nuts.
Normally, such apparatus include a transfer arm having a manipulator device or gripper connected to a transfer arm assembly, and an actuation assembly for moving the transfer arm in a preselected direction. The actuation assemblies most often used are electrically or pneumatically powered. The electrically powered apparatus are prone to failure due to the sophisticated electrical circuitry necessary to provide precise timed movement of the article. Consequently, such units require frequent maintenance and parts replacement, thereby increasing the manufacturing costs of a particular product. Pneumatically powered apparatus typically enjoy a greater life span than electrically powered assemblies. However, pneumatically controlled transfer apparatus are rarely used in applications requiring a high degree of positional accuracy because of their inability to accurately and dependably deposit the article in the desired location.
This lack of positional accuracy is most often encountered in industrial settings wherein the pneumatically actuated transfer apparatus is used in conjunction with other apparatus actuated by the same fluid pressure line, or where there is a large number of pneumatically operated transfer apparatus connected to the same fluid pressure line. In these situations, it is often difficult to precisely control the fluid pressure. As a result, the transfer apparatus experiences pressure fluctuations. When exposed to these pressure fluctuations, existing transfer apparatus will lose their grip on the article, causing the transfer arm to release the article while in transport. This inability to effectively transfer an article due to pressure fluctuations causes a decrease in efficiency, and often damages the article being transferred, thereby increasing material costs.
Additionally, many of these pneumatically controlled transfer apparatus require an additional mechanism to deposit the article once it is transported to its desired location. That is, a first cylinder is used to move the transfer arm from a first location to a second location, while a separately actuated, second cylinder is used to grasp and subsequently release the workpiece. This bifurcated operational sequence increases the complexity of the overall design of the transfer apparatus, and increases the probability of error given the imprecision associated with each cylinder.
Another problem confronting existing transfer apparatus is the tendency of the manipulator or gripper to rotate while in motion towards its target destination. This rotational movement of the gripper results in the inability of the transfer apparatus to provide proper placement of an article in applications where article orientation critical. Still another problem associated with existing transfer apparatus is their inability to accommodate parts of varying size without requiring the installation of a different gripper or manipulator. Substituting different grippers to accommodate articles of varying size requires the use of manual labor and necessitates placing the particular transfer apparatus off-line. Thus, in applications where there is a frequent change in article size, the costs associated with operating the particular assembly line are increased.
Consequently, there exists a need for a transfer apparatus for automated parts movement capable of reliably grasping and transporting an article, which can maintain the article in the proper orientation, and can accommodate articles of varying size without having to replace the ripper.
Accordingly, the present invention provides a transfer apparatus for automated parts movement which, in preferred form, comprises a cylinder with a pair of coaxial pistons operably attached to a transfer assembly which includes a gripper. The transfer apparatus can be actuated by any fluid commonly utilized in the art, but is preferably pneumatically actuated. One of the pistons is advanced to extend the transfer assembly and grip the article held thereby. The pistons are further advanced to move the transfer assembly, and the article held thereby, to a target destination. Further advancement of one piston causes the transfer assembly to release the article, and thereafter, both pistons are retracted. Consequently, the transfer apparatus of the present invention permits the grasping, transportation and deposition of an article to be accomplished using a pair of cooperating pistons, and thus eliminates the imprecision associated with transfer apparatus employing independent, separately actuated, piston assemblies to accomplish the grasping and transportation procedure.
According to one aspect of the invention, the transfer apparatus includes an enclosed cylinder sealed by a first and a second end. A first and a second fluid inlet port, in fluid communication with the interior of the enclosed cylinder, are located proximate to the first and second end, respectively. Slidably positioned within the cylinder is a first, or inner, piston which is slidably received by a second, or outer, piston. Attached to both the inner piston and outer piston is a transfer assembly equipped with a gripper extending through the second end of the cylinder. Introduction of fluid through the first inlet port moves the inner and outer piston axially within the cylinder, enabling the transfer assembly to grasp an article and subsequently move the article to a target destination. Continued introduction of fluid through the first inlet port results in the stripping or removal of the article from the transfer assembly. Once the article is removed from the transfer assembly, fluid is introduced through the second fluid inlet port, causing the retraction of the inner and outer pistons and thus, the transfer assembly to thereby complete the stroke. Employing a cooperating inner and outer piston, both of which are actuated by a single fluid source, maximizes the precision of the transfer apparatus.
According to another aspect of the invention, a transfer apparatus includes an enclosed cylinder having a first and a second end, and a pair of pistons slidably positioned within the cylinder. The pistons are operably connected to a transfer assembly. The transfer assembly includes a sheath attached to the piston assembly and extending through an opening in the second end of the cylinder, and an inner rod attached to the piston assembly and contained within the sheath. The rod is attached at its end to a gripper. Introduction of fluid through the first end of the cylinder effects movement of the piston assembly to sequentially extend the gripper beyond the end of the sheath, and move the inner rod, sheath, and gripper away from the second end of the cylinder. Introduction of fluid through the second end of the cylinder retracts the piston assembly, and moves the sheath, inner rod and gripper towards the first end of the cylinder. The transfer assembly of the present invention provides efficient and precise movement of articles to thereby increase the efficiency of the transfer process.
In a preferred embodiment, the gripper is a gripper assembly having a spring loaded jaw assembly threadably attached to the end of the inner rod. The use of a spring loaded jaw assembly enables the transfer apparatus of the present invention to be used to grasp articles of varying size without switching jaw assemblies. This in turn reduces the complexity and cost of the manufacturing operation. Additionally, threadably attaching the spring loaded jaw assembly to the inner rod prevents the spring loaded jaw assembly from rotating during transportation of the article. Hence, the article is maintained in the proper orientation to thereby enable its precise placement in the desired location. This feature permits the present invention to be used in applications wherein the orientation of the article must be maintained in order to fall within the clearances required by the particular manufacturing application.
These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.